Study of the Healing of the Fault Zone Ruptured in the 1992 Landers, California Earthquake by Monitoring Fault Zone Trapped Waves

本文利用便携式高性能地震仪监测断裂带陷波传播特征，研究1992年M=7.4兰德斯地震破裂断裂带的震后愈合。先前的研究显示了在兰德斯地震的断层带中存在地震导波的证据。根据捕获模式数据，沿破裂面分解出一个宽度为180 m的低速高衰减层。这一层在发震带从地表延伸到至少10公里深处。该层宽度沿断裂带纵向和横向变化较大，在断裂带弯曲处变得很窄。断裂带圈闭波的观测和模拟表明，圈闭波的幅值和频率内容对断裂带的速度结构和性质非常敏感。因此，通过监测断裂带捕获波振幅和频散特征的微小变化，可以探测地下断层在空间和时间上的变化。研究结果有助于进一步认识断裂带的构造、流变和本构关系、准静态成核到动态破裂的转变以及地震复发的模式和机制。这项研究是国家减少地震危害计划的一个组成部分。* * * ? ?

9404762 Li This research is to study the postseismic healing of the fault zone ruptured in the M=7.4 Landers earthquake of 1992 by monitoring propagation characteristics of fault zone trapped waves using portable high-capability seismometers. Previous work showed evidence for seismic guided waves trapped within the fault zone of the Landers earthquake. Based on trapped mode data, it resolved a low velocity, high-attenuation layer with a width of 180 m along the rupture plane. This layer extends from the surface to a depth of at least 10 km in the seismogenic zone. It was also found that the width of this layer varies vertically and laterally along the fault zone, and it becomes very narrow at the fault bend. Observations and simulation of fault zone trapped waves show that the amplitudes and frequency contents of these waves are very sensitive to the velocity structure and properties of the fault zone. Therefore, the subsurface fault variability in space and time can be detected through monitoring minor changes in amplitude and dispersion characteristics of fault zone trapped waves. Results from this study should advance understanding of fault zone structure, rheology and constitutive relations, the transition from quasistatic nucleation to dynamic rupture, and the models and mechanisms for earthquake recurrence. This research is a component of the National Earthquake Hazard Reduction Program. *** ??